In general, known electro-pneumatic converters include a two-armed balance beam mounted by a pivot bearing, a telescoping coil system engaging the balance beam, an electric current to be converted being applied to the coil in operation, and a nozzle connected to a pneumatic fluid source through a restrictor and arranged in front of a baffle plate surface of the balance beam to form a nozzle and baffle plate with the balance beam. The pressure ensuing at the nozzle acts on the baffle plate surface of the balance beam and counterbalances a torque exerted by the telescoping coil system on the balance beam due to the electric current.
In known electro-pneumatic converters (German Offenlegungsschrift No. 26 54 003, "Regelungstechnische Praxis" 22 (1980), 221 to 230, "Regelungstechnische Praxis" 23 (1981) 201 to 206 (FIG. 6) a balance beam is suspended easily rotatably by a flexural pivot. A telescoping coil is attached to the balance beam. The telescoping coil plunges into the air gap of a housing-fixed magnet. When a current is flowing through the telescoping coil, it is drawn into the magnet. Thereby it exerts a torque on the balance beam, which torque is proportional to the intensity of current. A nozzle is arranged in front of a surface of the balance beam and is connected to a pneumatic fluid source through a restrictor. This nozzle forms a nozzle and baffle plate with the balance beam. A pressure ensues at the nozzle, which pressure counterbalances a torque exerted by the telescoping coil system on the balance beam due to the electric current. This pressure can become effective on the balance beam through a diaphragm or a bellows. Compensation can, however, also be effected directly by the pressure in the nozzle. An equilibrium results in both cases.
The force on the telescoping coil system caused by the electric current to be converted is relatively small as compared to the force pneumatically exerted on the balance beam through a bellows or directly through the nozzle. Therefore, a relatively large mass, namely the telescoping coil, is necessarily located on a relatively large mass, namely while, on the other hand, a massless compensation takes place through a relatively small surface on a relatively small lever arm. To compensate for this imbalance of the masses, it is, therefore, usual to attach a counter-weight to the arm of the balance beam opposite to the telescoping coil, which counter-weight counterbalances the telescoping coil. The counter-weight is adjustable to be able to counterbalance other mass imbalances of the arrangement of the balance beam. This counter-weight does not contribute to the signal transmission. However, it deteriorates the dynamic transfer behavior of the electro-pneumatic converter. Therefore, conventional electro-pneumatic converters are susceptible to vibrations, that is, they have a tendency to oscillate, and are thus sensitive to shaking.
It is the object of the invention to reduce the susceptibility to vibrations and the sensitivity to shaking of an electro-pneumatic converter of the above defined type.